The invention relates to a method and an arrangement for operating an internal combustion engine having gasoline direct injection.
A method and an arrangement for operating an internal combustion engine with gasoline direct injection are described in DE 43 32 171 A1 (U.S. Pat. No. 5,483,934). In the control system disclosed there, the entire operating range of the engine is subdivided into various regions in accordance with rpm and load and, depending upon the actual operating region, the fuel is either injected during the induction stroke or during the compression stroke. With an injection during the induction stroke, a substantially homogeneous fuel distribution (homogeneous operation) results because of the time available until ignition as well as because of the swirling of the injected fuel by the inducted air flow; whereas, a stratified charge (stratified operation) arises in the case of injection during the compression stroke. In the homogeneous operation, the engine is operated throttled, that is, the air supply is limited by a throttle flap. In the stratified charge operation, the engine is operated virtually unthrottled, that is, the air supply through the throttle flap is virtually not limited. A switchover between these operating modes takes place in dependence upon the above-mentioned operating variables and/or on other predetermined criteria, for example, with respect to the power demands made by the driver.
It is an object of the invention to further optimize the operation of an internal combustion engine having gasoline direct injection.
This is achieved with the characterizing features of the independent patent claims.
With the state of the art mentioned initially herein, a switchover is always made for the entire engine between the individual operating modes thereof. Furthermore, all cylinders contribute uniformly to the torque of the engine. In this way, flexibility and degrees of freedom in the configuration of the control are surrendered.
A further optimization of the drive of a motor vehicle is achieved with an asymmetric operation of an internal combustion engine having gasoline direct injection, especially when the engine has at least two cylinder banks which can be controlled independently of each other.
It is of special advantage that, in operating states in which the power, which is wanted by the driver, can no longer be made available because of the low consumption stratified charge operation, only a part of the engine, for example, one cylinder bank is driven in the comparatively consumption-intensive homogeneous operation. The other cylinder bank continues to be operated with the low consumption stratified charge operating mode. In this way, on the one hand, the increased power demands of the driver can be made available while, on the other hand, the consumption is minimized. This advantage is also achieved in that the contribution of individual cylinder banks or cylinder groups to the total torque is pregiven differently.
A further advantage, which is achieved by such an asymmetric operation of the engine, is an improvement of the noise emission or generally of the comfort of the engine. It is especially advantageous in this context that, when clearing a storage catalytic converter in idle or in the part-load region, not all banks are switched over simultaneously. The noise emission is optimized by the alternating switchover.
Of special significance is further that more degrees of freedom in the configuration of the exhaust-gas concepts are available because of the asymmetric operation of the engine having gasoline direct injection. For example, the power request of the driver is converted in such a manner that one part of the engine is operated in an exhaust-gas optimal operating mode and at an exhaust-gas optimal operating point; whereas, the actual power demand of the driver is executed by the control of the operating point as well as, if required, the operating mode of another part of the engine.
Of special advantage is the application of the asymmetric operation in an internal combustion engine having gasoline direction injection with at least two cylinder banks having at least two throttle flaps controllable independently of each other. In an advantageous manner, this idea can also be applied in engines having only one throttle flap. The air charge is adjusted in such a manner that one portion of the cylinders is operated homogeneously and the other portion is operated in a stratified operating mode. The latter leads to a total increased air charge so that the throttle losses are reduced compared to a homogeneous operation of the entire engine.
In addition to the switchover between the operating modes with stratified charge and with homogeneous fuel mixture formation, the principle of the asymmetric operation of the engine is also applied between operating modes such as homogeneous stoichiometric, homogeneous lean or mixed operating modes such as an operating mode having double injection wherein a homogeneous fuel mixture arises as well as a stratified fuel mixture. Here too, the advantages which are achieved via the asymmetric operation are arrived at as described above.